The present invention relates to an improved ablation catheter that is particularly useful for ablating tissue in a tubular region of or near the heart.
Cardiac arrhythmias, and atrial fibrillation in particular, persist as common and dangerous medical ailments, especially in the aging population. In patients with normal sinus rhythm, the heart, which is comprised of atrial, ventricular, and excitatory conduction tissue, is electrically excited to beat in a synchronous, patterned fashion. In patients with cardiac arrhythmias, abnormal regions of cardiac tissue do not follow the synchronous beating cycle associated with normally conductive tissue in patients with sinus rhythm. Instead, the abnormal regions of cardiac tissue aberrantly conduct to adjacent tissue, thereby disrupting the cardiac cycle into an asynchronous cardiac rhythm. Such abnormal conduction has been previously known to occur at various regions of the heart, such as, for example, in the region of the sino-atrial (SA) node, along the conduction pathways of the atrioventricular (AV) node and the Bundle of His, or in the cardiac muscle tissue forming the walls of the ventricular and atrial cardiac chambers.
Cardiac arrhythmias, including atrial arrhythmia, may be of a multiwavelet reentrant type, characterized by multiple asynchronous loops of electrical impulses that are scattered about the atrial chamber and are often self propagating. In the alternative or in addition to the multiwavelet reentrant type, cardiac arrhythmias may also have a focal origin, such as when an isolated region of tissue in an atrium fires autonomously in a rapid, repetitive fashion.
A host of clinical conditions may result from the irregular cardiac function and resulting hemodynamic abnormalities associated with atrial fibrillation, including stroke, heart failure, and other thromboembolic events. In fact, atrial fibrillation is believed to be a significant cause of cerebral stroke, wherein the abnormal hemodynamics in the left atrium caused by the fibrillatory wall motion precipitate the formation of thrombus within the atrial chamber. A thromboembolism is ultimately dislodged into the left ventricle, which thereafter pumps the embolism into the cerebral circulation where a stroke results. Accordingly, numerous procedures for treating atrial arrhythmias have been developed, including pharmacological, surgical, and catheter ablation procedures.
Several pharmacological approaches intended to remedy or otherwise treat atrial arrhythmias have been disclosed, although such pharmacological solutions are not generally believed to be entirely effective in many cases, and may in some cases result in proarrhythmia and long term inefficacy. Several surgical approaches have also been developed with the intention of treating atrial fibrillation. One particular example is known as the xe2x80x9cmaze procedure,xe2x80x9d as is disclosed by Cox, J L et al. in xe2x80x9cThe surgical treatment of atrial fibrillation. I. Summaryxe2x80x9d Thoracic and Cardiovascular Surgery 101(3), pp. 402-405 (1991). In general, the xe2x80x9cmazexe2x80x9d procedure is designed to relieve atrial arrhythmia by restoring effective atrial systole and sinus node control through a prescribed pattern of incisions about the tissue wall. In the early clinical experiences reported, the xe2x80x9cmazexe2x80x9d procedure included surgical incisions in both the right and the left atrial chambers. However, more recent reports predict that the surgical xe2x80x9cmazexe2x80x9d procedure may be substantially efficacious when performed only in the left atrium.
The xe2x80x9cmaze procedurexe2x80x9d as performed in the left atrium generally includes forming vertical incisions from the two superior pulmonary veins and terminating in the region of the mitral valve annulus, traversing the inferior pulmonary veins en route. An additional horizontal line also connects the superior ends of the two vertical incisions. Thus, the atrial wall region bordered by the pulmonary vein ostia is isolated from the other atrial tissue. In this process, the mechanical sectioning of atrial tissue eliminates the precipitating conduction to the atrial arrhythmia by creating conduction blocks within the aberrant electrical conduction pathways.
While the xe2x80x9cmazexe2x80x9d procedure as reported by Cox and others has met some success in treating patients with atrial arrhythmia, its highly invasive methodology is believed to be prohibitive in most cases. However, these procedures have provided a guiding principle that mechanically isolating faulty cardiac tissue may successfully prevent atrial arrhythmia, and particularly atrial fibrillation caused by perpetually wandering reentrant wavelets or focal regions of arrhythmogenic conduction.
Success with surgical interventions through atrial segmentation, particularly with regard to the surgical xe2x80x9cmazexe2x80x9d procedure just described, has inspired the development of less invasive catheter-based approaches to treat atrial fibrillation through cardiac tissue ablation. Examples of such catheter-based devices and treatment methods have generally targeted atrial segmentation with ablation catheter devices and methods adapted to form linear or curvilinear lesions in the wall tissue which defines the atrial chambers, such as those disclosed in U.S. Pat. No. 5,617,854 to Munsif, U.S. Pat. No. 4,898,591 to Jang et al., U.S. Pat. No. 5,487,385 to Avitall, and U.S. Pat. No. 5,582,609 to Swanson, the disclosures of which are incorporated herein by reference. The use of particular guiding sheath designs for use in ablation procedures in both the right and/or left atrial chambers are disclosed in U.S. Pat. Nos. 5,427,119, 5,497,119, 5,564,440, and 5,575,766 to Swartz et al., the disclosures of which are incorporated herein by reference. In addition, various energy delivery modalities have been disclosed for forming such atrial wall lesions, and include use of microwave, laser, and more commonly, radiofrequency energies to create conduction blocks along the cardiac tissue wall, as disclosed in WO 93/20767 to Stem et al., U.S. Pat. No. 5,104,393 to Isner et al., and U.S. Pat. No. 5,575,766 to Swartz et al, respectively, the disclosures of which are incorporated herein by reference.
In addition to attempting atrial wall segmentation with long linear lesions for treating atrial arrhythmia, ablation catheter devices and methods have also been disclosed that are intended to ablate arrhythmogenic tissue of the left-sided accessory pathways, such as those associated with the Wolff-Parkinson-White syndrome, through the wall of an adjacent region along the coronary sinus. For example, Fram et al., in xe2x80x9cFeasibility of RF Powered Thermal Balloon Ablation of Atrioventricular Bypass Tracts via the Coronary Sinus: In vivo Canine Studies,xe2x80x9d PACE, Vol.18, p 1518-1530 (1995), disclose attempted thermal ablation of left-sided accessory pathways in Jo dogs using a balloon that is heated with bipolar radiofrequency electrodes positioned within the balloon. Additional examples of cardiac tissue ablation from the region of the coronary sinus for the purpose of treating particular types of cardiac arrhythmias are disclosed in: xe2x80x9cLong-term effects of percutaneous laser balloon ablation from the canine coronary sinusxe2x80x9d, Schuger C D et al., Circulation (1992) 86:947-954; and xe2x80x9cPercutaneous laser balloon coagulation of accessory pathwaysxe2x80x9d, McMath L P et al., Diagn Ther Cardiovasc Interven 1991; 1425:165-171.
Less-invasive percutaneous catheter ablation techniques have been disclosed which use end-electrode catheter designs with the intention of ablating and thereby treating focal arrhythmias in the pulmonary veins. These ablation procedures are typically characterized by the incremental application of electrical energy to the tissue to form focal lesions designed to interrupt the inappropriate conduction pathways. One example of a focal ablation method intended to destroy and thereby treat focal arrhythmia originating from a pulmonary vein is disclosed by Haissaguerre, et al. in xe2x80x9cRight and Left Atrial Radiofrequency Catheter Therapy of Paroxysmal Atrial Fibrillationxe2x80x9d in Journal of Cardiovascular Electrophysiology 7(12), pp. 1132-1144 (1996). In another focal ablation example, Jais et al. in xe2x80x9cA focal source of atrial fibrillation treated by discrete radiofrequency ablationxe2x80x9d Circulation 95:572-576 (1997) applies an ablative technique to patients with paroxysmal arrhythmias originating from a focal source.
U.S. Pat. Nos. 6,024,740 and 6,117,101 disclose catheters for ablating a circumferential lesion in the pulmonary vein or other region. The catheters include a circumferential ablation element comprising an expandable balloon and an ablation element, such as an ultrasound transducer, coupled to the expandable balloon. The ablation element couples to the balloon""s outer skin to ablate a circumferential path of tissue engaged to the balloon. This arrangement has been found effective for creating the desired circumferential ablation. However, it would be desirable to provide a mechanism to enhance stabilization of the ablation element in the pulmonary vein or other region. It would also be desirable to provide a mechanism for controlling the size and shape of the balloon to enhance the stabilization of the balloon and the contract with the tissue in the pulmonary vein. It would also be desirable to provide a mechanism for controlling the precise position of the ablation element once the catheter is positioned in the heart.
The present invention is directed to an improved catheter having a circumferential ablation element surrounded by an inflatable balloon that includes a mechanism for changing the shape of the balloon once expanded. The inventive catheter is particularly useful for treatment within a tubular region of or near the heart, e.g., a pulmonary vein, the coronary sinus, the superior vena cava, or the pulmonary outflow tract.
In one embodiment, the catheter comprises an elongated tubular catheter body having an outer wall, proximal and distal ends, and a lumen extending therethrough. The catheter also comprises a generally tubular inner support member having proximal and distal ends and a lumen extending therethrough. A proximal portion of the inner support member extends into the lumen of the catheter body, and a distal portion of the inner support member extends outside the catheter body. A circumferential ablation element, such as an ultrasound transducer, is mounted on the distal portion of the inner support member outside the catheter body. A moveable tube extends through the lumen of the inner support member and through the catheter body. The moveable tube is longitudinally moveable relative to the inner support member and catheter body and has a distal end that extends beyond the distal end of the inner support member. An inflatable balloon is provided generally in surrounding relation to the circumferential ablation element. The inflatable balloon has a proximal end attached, directly or indirectly, to the distal end of the catheter body and a distal end attached, directly or indirectly, to a portion of the moveable tube that extends beyond the distal end of the inner support member. Longitudinal movement of the moveable tube relative to the catheter body and inner support member causes movement of the distal end of the balloon relative to the proximal end of the balloon to thereby change the length and shape of the expanded balloon.